 
   Usage:
 
-  (defn my-f
-    [a-val b-val]
-    ... some computation on a and b in here)
-
-  (on-changes my-f [:c]  [:a] [:b])
+      (defn my-f
+        [a-val b-val]
+        ... some computation on a and b in here)
+
+      (on-changes my-f [:c]  [:a] [:b])
 
   Put this Interceptor on the right handlers (ones which might change :a or :b).
   It will:


  These handlers take two arguments;  `coeffects` and `event`, and they return `effects`.

  (fn [coeffects event]
     {:db ...
      :dispatch ...})

   Wrap handler in an interceptor so it can be added to (the RHS) of a chain:
     1. extracts `:coeffects`

  "Returns an interceptor which wraps the kind of event handler given to `reg-event-ctx`.
  These advanced handlers take one argument: `context` and they return a modified `context`.
  Example:

      (fn [context]
         (enqueue context [more interceptors]))"
  [handler-fn]
  (->interceptor
    :id     :ctx-handler
